The striker came off the bench with just minutes remaining and won the ball in the visitors’ half before firing emphatically past the Hornets’ goalkeeper.

Harris’ goal secured a massive three points in the U’s quest for Championship survival after Myles Peart-Harris had put the hosts ahead in the first half.

“Huge,” the Wales international emphasised after the game.

“Going off the two games we played over Easter, as a team we thought we should have had six points. We didn’t lose the games – if you can’t win, don’t lose.

Mark Harris fires Oxford United to a 2-0 win over Watford (Image: Oxford United)

“Coming into this game, we knew how much of a big game it was and we’ve gone out there, put a performance and got the three points and that’s what we need at the minute.

“Where we are in the league, last 10 minutes and still 1-0, anything can happen in the Championship, but I thought we defended excellently from the front today.

“Will Lankshear, Jamie Donley, both wide men, all as a team I thought they were excellent.

Myles Peart-Harris wheels away after scoring for Oxford United (Image: Oxford United)

“It was nice to have a game where we were 1-0 up and just keeping them in their half, not just defending all game. To get the second goal was nice because then you can take a breather and see the three points over the line.”

Harris had a lot of time and space on the ball after winning it high up and was able to pick out the bottom corner in style.

He explained: “To be honest, I thought I was a bit too wide, but once I got the second touch on the ball I could just see the goal, so it was just hit it and hope. Get it across the face of goal and hopefully it goes in, and it did so happy days.

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Mark Harris celebrates scoring against Watford (Image: Oxford United)

“Today was brilliant and I’m buzzing. Hopefully now we can kick on, four more games, get as many points as we can and let’s see where it leaves us.”

The Welshman was also refreshing when asked if Portsmouth’s late winner at Middlesbrough hurt to see.

“I’m not going to lie and say no it doesn’t because it does,” Harris admitted.

“They’re down there with us and we want to be above the bottom three so we’re obviously going to look at results. But it’s down to us to take care of our own job. If we keep winning, we’ll be fine.”

Oxford now sit 22nd in the league, one point from safety.

Myles Peart-Harris and Mark Harris scored the goals to defeat the Hornets at the Kassam and maintain their survival push going into the final four games of the Championship season.

The U’s were the better team on the day, looking more dangerous in forward areas and keeping the visitors as arm’s length for the vast majority of the game.

“We haven’t been good enough, basically,” Still summarised.

“The performance there, we haven’t matched Oxford in terms of aggression, in terms of adapting to this type of game at this moment of the season.

Watford manager Edward Still (Image: Steven Paston/PA Wire)

“Everything becomes more intense, more power-based, and we haven’t been able to deal with it well enough and to lose the game on a set-piece, second ball, a very similar goal to what we’ve conceded against Charlton only a few days ago, and then for it to be killed off by a mistake at the end there is extremely frustrating.

“It makes you angry and all the rest of those negative emotions.

“I think everybody had that feeling that we haven’t been able to match them and to create a sufficient amount of moments in the game where we could dictate the play,” the brother of former Southampton boss, Will Still, continued.

Oxford United’s Stan Mills battles for the ball (Image: Oxford United)

“There’s been a period in the first half, there’s been a period in the second half, but overall it’s not enough.

“They’ve just exploited their strengths to the utmost. Taking that set-piece goal early on and the pitch, with the bobbly pitch that it is, the wind as it is, all of those factors, they’ve dealt with everything and done much better than what we have.”

Matt Bloomfield celebrates Oxford United’s win over Watford (Image: Oxford United)

After the win, Matt Bloomfield’s Oxford move up a place to 22nd in the table, Gary Rowett’s Leicester City having been defeated by Swansea City at home, and one point from safety.

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Rivals Portsmouth pulled off a dramatic 1-0 win in the dying moments at the Riverside Stadium against Middlesbrough to keep themselves a singular point above the U’s.

United have a week to prepare for their next match, a trip to Derby County who were beaten by Saints at the weekend.

There is hope that Jack Currie will be well enough to return to the squad after it was confirmed that he would undergo surgery on his ankle at the end of the season.

Nik Prelec, who rolled his ankle last week in training and missed the Watford win, is also hopeful for the journey to Pride Park.

The U’s swatted away the Hornets thanks to a first-half goal from Myles Peart-Harris and a 92nd-minute finish from Mark Harris to pick up a huge three points in their quest for Championship survival.

Oxford dispelled their recent trends of conceding early and dropping points late on as the Yellows boss acknowledged the weight of Saturday’s victory.

“It was crucial today, especially considering the magnitude of the situation that we’re in,” Bloomfield confirmed.

“We have to try and maximise every opportunity, but we’re certainly not getting carried away. We’re still below the line.

Cameron Brannagan celebrates Mark Harris scoring for Oxford United (Image: Oxford United)

“We’ve got a lot of work still to do, but we’re giving ourselves a real chance.

“I think we would have taken that a few games ago to be where we are and still fighting and having given ourselves the opportunity that we have, but…there’s plenty more work still to do.

“I said to the lads before the game, big players, big characters stepped forward and I thought we had a few that really stepped forward today.

(Image: Oxford United)

“The most important thing was getting three points today…but I don’t see how you do that without chasing the performance.

“So the performance today is really satisfying, especially second half.

“[In the] second half, to play with the energy and the intent, I thought there was a real intent about us.

Oxford United’s Ciaron Brown wrestles Watford’s Luca Kjerrumgaard for the ball (Image: Oxford United)

“It would have been obviously very nice to try and get the second a little bit earlier to make it a bit more comfortable because at 1-0, with opposition the calibre of Watford, the individual players that they have, it can turn at any moment.

“Our football intelligence tells us they’re going to have a little spell at some point and at 1-0, one moment can change your afternoon from elation to frustration.

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“I was a little bit nervous that defending a one-gone lead, there’s just one instant that could go the other way. We wanted to try and get that second and make it more comfortable and obviously it came pretty late. It would have been nice to come back a bit earlier.

United are certainly still in the fight with four more Championship games remaining.

“It certainly looks like a team that believes in each other and in themselves and what they’re doing.

“It takes time to work on these things. The level of our performance in the last couple of months…has been fairly good.

“But you can also lose it as quickly as you can find it. So we have to cherish it, I think, and keep working at it because we don’t want to lose it.”